1. Field of the Invention
The present invention relates to grain treatment, and more particularly to systems and methods for treating grain in grain piles with ozone.
2. Background and Related Art
Many types of grain are grown for human and animal consumption and use. The condition of the grain is often affected by the growing conditions, and when the grain is harvested, it may be found to contain insects, mold and/or bacteria, unwanted odors, and/or toxins remaining from the presence of molds and the like. Additionally, once grain has been harvested, it often is stored for some time prior to final distribution and use. During times of storage, existing problems with the grain can be exacerbated. Depending on the extent and severity of the odor, mold, or toxin problems, the value of the grain can be slightly to greatly reduced.
Several forms of mycotoxins can be found in harvested and/or stored grain, including vomitoxin, aflatoxin, and fumonisin. These toxins are residues left behind by molds that may no longer be present in the grain. Certain conditions during certain periods of the grain growth cycles encourage mold growths, and the toxins are the after-products of that growth. It is essentially impossible to spray or treat the growing grain in such a way as to treat or prevent the mold outbreaks. Therefore, farmers generally have to hope for favorable growing conditions that do not encourage mold proliferation.
In Europe, statutory levels of a range of mycotoxins permitted in food and animal feed are set by a range of European directives and Commission regulations. The U.S. Food and Drug Administration has regulated and enforced limits on concentrations of mycotoxins in foods and feed industries since 1985. Vomitoxin is a common problem in smaller grains such as wheat and barley. Aflatoxin is affects the marketability of corn and peanuts. Fumonisin is problematic in corn crops.
Deterioration in the quality of stored grain by insects, molds and mycotoxins causes economic losses to farmers, elevators managers and processors throughout the world. Insect development in stored grains is a function of time, grain moisture content and grain temperature. The current trend is toward a reduction in the dependence on chemicals. Aeration is one non-chemical alternative to reduce insect problems. The use of aeration contributes towards a safer environment by reducing the chemical residues in the food and feed supply chains, but is still limited in its ability to adequately address grain storage needs, especially in large grain piles.
Elevator operators regularly pile grain outdoors for a few weeks or months when receipts at harvest temporarily exceed storage capacity and when transportation is not available to move the grain ahead in the marketing chain. Usually outdoor piles store grain for periods not exceeding 6 months before grain is moved or marketed. To maintain grain quality, it should be placed in the pile with a temperature below 15.5° C. and safe storage moisture content of 15% or less. Sufficiently-dry corn stored in piles during only the cooler fall and winter weather may not need to be covered and aerated; however, when grain is stored into the following spring and summer, tarp covers are commonly used and provisions need to be made for aeration.
If the grain must be piled outside on the ground, drainage is crucial. The pile should be on high ground and the earth crowned under the pile. A vapor barrier (for example 6-mil plastic) is typically placed on the ground to keep ground moisture from wetting the grain unless the pile is on well-drained gravel-covered soil.
Grain depth in an outdoor pile frequently runs from near zero at the edge of the pile to a maximum at the center. A circular pile that will hold one million bushels may be slightly less than 300 feet in diameter with a circumference of over 900 feet. An oblong pile may be 120 to 180 feet wide and 300 to 700 feet long, holding one-half to one and one-half million bushels. Often some type of low retainer wall is used around the circumference, such as concrete traffic dividers or barriers. The weight of the concrete is such that the barriers are stable and support the lateral pressure of the grain up to depths of 3-4 feet. With a 5 foot grain wall depth, there is a force of about 115 pounds of force on each foot pushing outward.
Plastic or tarp covering a pile reduces wetting by rain and snow but may turn out to be an expensive, frustrating and labor-intensive undertaking. The top surface should be smooth to aid in drainage. The cover is placed to carry water away from the piled grain to prevent wetting the grain. Condensation under the plastic may cause severe problems unless it is properly controlled with aeration. Airflow underneath and near the cover reduces the condensation and carries the moisture away. Commonly, multiple aeration fans exhaust air from the bottom of the pile. Sucking air with the fans through the pile and out of the bottom also aids in holding the tarp, plastic, or other covering down in windy situations.
The problem of getting adequate distribution of aeration air to grain in a large pile is obvious. For example, a circle at 30 feet in from the edge of the circular one million bushel pile described above has a circumference of approximately 750 feet. The general recommendation on duct spacing is that ducts should be spaced no farther apart than the grain is deep, 15 feet in this example. Thus, 48 ducts and fans would be required for this pile. Without a cover, the air entrance area for a suction aeration system is the entire grain surface. One problem in aerating tarp-covered piles is caused by the tarp. The tarp is held in place through suction created by the aeration fans; however, if the tarp is held too tightly against the grain surface, no air will enter the grain pile, and aeration will be minimized. If a center tower is employed to fill the storage, aeration ducts and/or exhaust fans can be part of the center structure. The aeration air may be drawn in through a perforated retainer wall and exhausted out of the center tower, or vice-versa.
Aeration requires a mechanical ventilation system that can be used to manage grain temperatures by moving air with the desired properties through the grain mass preventing moisture movement and accumulation therefore maximizing grain storage life. In North America, numerous aeration system designs exit to aerate large outdoor grain piles. The main purpose of aeration is to cool grain by moving air through the grain mass by suction (negative pressure) or by pushing (positive pressure). In order to achieve cooling as uniformly and quickly as possible, an aeration system design must provide as uniform of an air distribution through the grain mass as possible. The most common aeration method in outdoor grain piles is by suction airflow in order to hold in place the tarps or other covering of the piles.
Even with the best aeration systems, however, problems still develop in the grain piles, and the value of some or all of the grain may be significantly reduced. Such problems develop and worsen over time. The full extent of the problems is often not discovered until the time of removing the grain from the piles for marketing and distribution. The scope of such problems can be understood by recognizing that a problem that causes a ten-cent-per-bushel average reduction in the value of the grain stored in a one million bushel pile equates to an economic loss of $100,000.00 dollars.